Lithography has been a cornerstone for continued scaling of electronics, all the way from micron-sized transistors in the ’80s to 45 nm transistors in the current technology. Lithography for manufacturing has been primarily using optical techniques (rather than other types like electron beam, x-ray, ion-beam) where light of a certain wavelength is used to project an image on a wafer using a photomask inbetween the light source and the wafer. Current lithography in chip manufacturing uses a 193 nm wavelength source, and feature sizes as small as 40 nm are possible by using a combination of advanced techniques such as phase shift masking, double patterning, and wet lithography. Though the resolutions achieved are impressive, mask costs have risen due to the complexity. In addition, getting feature sizes below 30 nm will be an uphill task using 193 nm sources. Thus there is a push toward EUV lithography which uses 13.6 nm sources. At this small a wavelength, a quartz lens will absorb light than diffract it - thus all lenses for EUV are reflective, thereby increasing the cost and complexity through the roof.
Three papers on the recent issue of Science (May 15) detail various approaches to achieve sub-wavelength features using simpler techniques. Though the transition of these techniques to manufacturing is too early to predict, there is hope that these techniques will atleast enable cheaper and faster low-volume fabrication like that needed in R&D.
Dr. Perry from Georgia Tech writes…”The main concept behind the “subdiffraction” resolution approaches reported in this issue is the use of dual exposures to create a spatial exposure pattern. These beams can have a donutlike pattern—the beam that activates the patterning chemistry is surrounded by a ring of intensity of another beam that suppresses the activation while maintaining a valley (or node) at the center of the activating beam. The product of the activation peak and “deactivation” donut pattern gives a spatial dosing pattern that is substantially finer than the far-field diffraction pattern of a tightly focused optical beam.”
Two-Color Single-Photon Photoinitiation and Photoinhibition for Subdiffraction Photolithography
Timothy F. Scott, Benjamin A. Kowalski, Amy C. Sullivan, Christopher N. Bowman, and Robert R. McLeod (15 May 2009) Science 324 (5929), 913. [DOI: 10.1126/science.1167610]
Confining Light to Deep Subwavelength Dimensions to Enable Optical Nanopatterning
Trisha L. Andrew, Hsin-Yu Tsai, and Rajesh Menon (15 May 2009) Science 324 (5929), 917. [DOI: 10.1126/science.1167704]
Achieving {lambda}/20 Resolution by One-Color Initiation and Deactivation of Polymerization
Linjie Li, Rafael R. Gattass, Erez Gershgoren, Hana Hwang, and John T. Fourkas (15 May 2009) Science 324 (5929), 910. [DOI: 10.1126/science.1168996]